Transfer system for liquid metals

ABSTRACT

Transfer system for liquid metals such as aluminum, zinc and magnesium. The system is used to transfer liquid metal in a casting process from a furnace to a casting machine while extending the life term of the transfer conduit. The canal replaces the use of gas burners with electric heat generating means in order to maintain the constant temperature of the liquid metal transferred. The system allows to automatically maintaining the liquid metal level and a constant temperature during said liquid metal transfer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a transfer system for liquid metals such as aluminum, zinc and magnesium. The invention also refers to a canal used in the transfer of such liquid metals and a method of transferring liquid metals using the transfer system.

2. Description of the Related Art

The use of canals in the transfer of liquid metals from the furnace to the casting machine is widely known and used. In the past, these canals were made of refracting concrete but the use of such material generated a great loss of temperature in the liquid metal during its transfer. Due to the enormous amount of materials available nowadays, there are at least two conditions that must comply when choosing the correct material in the process of making the canals. The first condition that a chosen material chosen must comply is that the loss of temperature of the liquid metal when transferred from the furnace to the casting machine must be minimum. The second condition that a chosen material must meet is the resistance to chemical attack deriving from the molten metal transferred.

Most of the processes that in the past where made inside the furnace were converted into continuum process incorporating specific equipments for filtering and removing contaminating gases for the metal. Due to this modification, the length of the canals transporting the melted metal had to be lengthened, increasing therefore the loss of temperature during the transfer of liquid metal. In order to reduce such loss of temperature, the common solution was to increase the temperature of the liquid metal at the furnace, rendering a reduced loss of temperature of the liquid metal during its transfer. However, this obvious solution made the liquid metal to oxidize at a faster rate, rendering it to a more chemical aggressive material hence reducing the life of the canals. It is also important to mention that the increase of temperature in the liquid metal generated the incorporation of several contaminants such as hydrogen which solubility increased with the rise of the temperature.

At the late 70's, ceramic fibers were incorporated into the world of technological material. By using ceramic fibers in the construction of canals, the results of durability were surprisingly increased. However, the use of such canals was only useful in short casting process usually lasting between 4 to 5 hours. After that period the canals had to be replaced. As the use of aluminum was increased over time, the industry developed new equipments known as continuous casting machines, where the duration of the casting process can last up to several days.

The problem encountered, when using the canals made of ceramic fiber in the continuous casting process, was that after every casting period the canals had to be replaced, therefore generating an increase in the final cost of the product. A partial solution to such problem was to develop canals using materials with increased resistance to the chemical attack but the problem encountered then was that using such materials also increased the loss of temperature in the liquid metal. Therefore, the canals included improved thermal insulation in order to obtain a satisfactory result. However, at the beginning of the continuum casting process the use of gas burners had to be applied in such process. Gas burners are widely known and use in the casting process, but it is also widely known that the expose of a material to a constant and powerful flame stream reduced the life term of such material producing cracks and clefts. Alternatively, in the near zones of the burners it could be found a temperature difference within several hundreds of degrees which generates tensions and micro cracks shortening the life term of the canal. In order to avoid the use of gas burners to maintain the temperature with in the canal, the use of electrical heaters were implemented reducing the deterioration of the canal.

Due to the constant deterioration of the canals and the casting equipment where the liquid metal passes through, the maintenance schedule to follow in order to continue with the normal casting procedure requires several stopping times, which is inadmissible in continuous casting process. By using conventional canals, the average temperature of the liquid metal is sometimes greater than 100° C. which is more that the normal temperature needed for casting. This represents a loss of 5° to 10° C. by meter in the length of the canal. This loss of temperature can also generate the reduction or even the loss of the casting process. In the event that the casting process includes several hours, the interruption of a casting process due to parametrical miscalculations in the process can generate an important economic damage.

As stated before, transferring canals are made of ceramic fibers and the same are placed in a metal cradle which is used to support the canal and abut the canal with an adjacent one by means of a bridle in order to conform a full canal for transferring the liquid metal. Another important factor to consider is the great difference between the thermal expansion coefficient of the canal and the metal cradle, which generates metal leaks in the junction between abutting canals increasing the leakage during several casting processes.

Another important factor to consider is the level of the liquid metal during the transfer between the furnace and the casting machine. When the liquid metal gets in contact with the mould a thin layer of solid is formed which contains the remaining of the liquid metal. This is a dynamic process where the solid layer generated is removed at constant speed and the new liquid metal arrives at the mould. The quality of the obtained piece depends mostly on the stability of the solid/liquid interaction and its contact with the mould in the process of solidification. The variation in the metal level at the feeding system of the moulds modifies the liquid pressure and disarrays the contact between the thin solid layer and the mould. The final result becomes a noticeable reduction in the length of the casting process

SUMMARY OF THE INVENTION

The present invention relates to a transfer system for liquid metal from a furnace to a casting machine wherein the system lengthens the life term of the transfer canal while used on several casting process.

The present invention also relates to a transfer canal to be used for transferring liquid metal from a furnace to a casting machine wherein the canal replaces the use of gas burners in order to maintain the constant temperature of the liquid metal transferred.

In accordance with still another important feature of this invention, it provides a method for controlling the liquid metal transfer between a furnace and a casting machine allowing to automatically maintaining the liquid metal level during said liquid metal transfer.

The above-discussed and other features and advantages of the present invention will be appreciated and understood by those of ordinary skill in the art from the following detailed discussion and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, wherein like elements are numbered alike in the several FIGURES:

FIG. 1 a schematic view of the system in accordance with the present invention;

FIG. 2 is a front elevation view, partly in cross-section, of a canal in accordance with the present invention;

FIG. 3 is a schematic drawing of the use of the method of the present invention with the system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1 the transfer system of the present invention comprises a central operation panel 2 which controls and commands a PLC (Programmable Logic Controller) 3. As stated on FIG. 1, the PLC controls the performance of a hydraulic central 4 which commands the movement of a balanced valve 5. This balanced valve actuates on a hydraulic cylinder 6 controlling the tilt of a casting furnace 7.

A laser sensor 8 detects the liquid metal level in the conduit 9 when the liquid metal is poured from the furnace 7 towards the casting machine 22 (FIG. 3). The data acquired by the laser sensor 8 is sent to the PLC 3 to adjust the furnace's tilting. The sensor 8 must be configured to detect the presence of liquid metal at a pre settled level bearing that the level 0 is the base of the canal. Said level can be settled according to the specific configuration of the casting process. The laser sensor 8 should be placed near the outlet of the furnace 7 but said sensor 8 can be used in any available position where it can be determined the level of the liquid metal in the conduit 9.

Making reference to FIG. 3, the conduit 9 is build based on a plurality of adjacent canals 10 abutted each other by means of nuts and bolts. Between every abutment a compressible gasket 11 made of ceramic fiber is placed in order to reduce the leakage of the liquid metal once is transferred from the furnace 7 towards the casting machine 22. Any skilled in the art could notice that the use of bolts and nuts as a mean for abutting several canals 10 in order to make the conduit 10 is just an example and that any means for joining two or more canals such as welding, riveting, clinching and so, can be used without leaving the scope of the present invention. However, it is preferable to use any means to adjoin two or more canals that will allow performing a fast replacement of the damaged canals and thus maintaining the modular condition of the conduit 9.

The canal 10 showed in FIG. 2 comprises a first U shape profile 12 in which a second U shape profile 14 is placed, being separated both profiles by an insulate layer 13. The profile 14 defines a path for the liquid metal to be transferred from the furnace 7 to the casting machine 22. In the present embodiment, the first profile 12 is made of a steel alloy while the second profile 14 is made of a refracting ceramic material. Moreover, the insulated layer 13 can be made of any insulate material such as fiber glass, ceramic fiber, microporous insulation panels, asbestos, refracting mud or the combination thereof. A lid 15 is placed on top of first and second profiles protecting the edges of such profiles from breakage when cleaning the conduit 10 once the casting process is over.

As seen on FIG. 2, a cover 17 is attached with a hinge 18 to the first profile 12. The cover is actuated by pneumatic or hydraulic means (not shown) controlled by said PLC 3. Said cover includes heat generating means 16 attached to the internal portion of the cover by an insulate layer 19. The insulate layer 19 can be made of the same material as the insulated layer 13. Said heat generating means 16 are defined by electric resistance heating elements 20 enclosed in metal tubes that emit heat in the form of infrared rays. Even though the number of electrical resistance heating elements 20 illustrated in FIG. 2 are only two, the number of such heating elements 20 can be as many as needed depending on the particular casting process. On the other hand, even if it is possible to replace said heating elements 20 with gas burners, the use of such gas burners can compromise the safety of the whole casting line. However, the use of heating elements 20 as means for generating heat in the canals 9 cannot be considered as limiting the scope of the invention, since it will be obvious to any skilled in the art replacing the heating elements 20 by any other heating source available. As seen on FIG. 3, the transfer system of the present invention comprises at least two heat sensors 23. Said sensors 23 are placed preferably one near the outlet of the furnace 7 and the other near the inlet of the casting machine 22. This sensor deployment allows the system to strictly control any differential of temperature along the total transfer of the liquid metal over the conduit 10. It can be appreciated that the use of more than two heat sensors is included within the bound of the scope of the invention, since it will be obvious to any skilled in the art to notice that the greater the number of heat sensors the better the result in maintaining the temperature level would be. On the other hand, the heat sensors 23 can be any sensor commercially available such as laser beam sensor, thermocouple or a combination of both.

From the safety point of view, the transfer system includes a complex electrical wiring (not shown) including current and voltage detectors that controls any variation such as in the heating elements 20 or heat sensors 23, allowing the operator of the casting line to control the temperature process. As it is shown in FIG. 2, canals 9 are placed over a double T beam 21. Such beam 21 is used as a strong and firm support platform for the total length of the conduit 10.

For a better comprehension of the present invention, an explanation of the use and functionality of the whole system will be explained in detail using all the figures mentioned before. As every casting process, the same begins at the furnace 7. The metal in liquid form is placed inside said furnace 7 kept at a melting point until it is ready to be poured in the conduit 10. For the present embodiment, the casting process will be explained using aluminum as the metal to be transferred. The aluminum in liquid form is kept in the furnace at approximately 720° C. Once the furnace 7 is tilted the pouring of the liquid metal in the conduit 10 occurs. This pouring method is based on a gravity pouring and the tilting degree is graduated and maintained by the hydraulic cylinder 6. Once the furnace 7 is tilted and the pouring begins, the laser sensor 8 controls the level of the metal poured and acquires data about the minimum and maximum levels and sends them to the PLC unit 3. The PLC unit then verifies that said data sent by the sensor 8 is within the parameters already configured in the PLC unit. In the event that the data sent by the sensor 8 is either over or below the parameters configured, the PLC unit sends the instructions to the hydraulic central 4 to command, by means of the balanced valve 5, the corresponding hydraulic cylinder 6 to either increase or decrease the tilt degree of the furnace 7. Once the data sent by the sensor 8 is within the parameters configured in the PLC unit, the tilting of the furnace 7 stops.

Once the liquid metal starts flowing through the conduit 10 in order to reach the casting machine, the breach in the temperature from the furnace's outlet and from the casting machine's inlet is increased proportionally to the length of the conduit 10. Therefore, sensors 23 gather the temperature in both places and each one sends the information to the PLC unit. The PLC unit compares the data received with the parameters previously configured. In the event that the temperature drops a few degrees, the PLC unit sends the instructions to a hydraulic center (not shown) which commands the closing of the covers 17 in order to reduce the loss of temperature. If the temperature keeps dropping the sensors 23 detect such drop and send the information to the PLC unit. Afterwards, the PLC unit processes the information and controls the ignition of the heating elements 20 in order to rise and maintain the heat of the liquid metal within the temperature parameters. In order to keep the temperature as homogenous as possible in the total length of the conduit 10, the PLC unit can individually control the ignition of the heat elements 20 in each canal 9, thus keeping a stricter control on the temperature range.

Once the casting procedure is finished, which as stated before it could last several days, the maintenance routine commences. This routine comprises the complete checking and control of each and every canal 9. In the event that one or more canals 9 show any sign of major attrition such canal can be easily replaced by a new one thanks to the modular construction concept that the conduit 10 has. On the other hand, if one or more canals 9 shows any small sign of ware, such as cracks in the ceramic fiber surface in the second profile, the same can be replaced in situ. This is possible since each canal has an easy construction configuration which allows the replacement of any part involved in the construction of the canal 9. As experience shows, the second profile is the part which suffers greater deterioration between several casting processes. Fixing in situ or replacing such second profile reduces the costs of maintenance of the casting process.

Finally, it is important to mention that even though the length of the canals 9 was not mentioned, the same can vary depending on the casting line to be used and also said canals can be formed in different shapes, not only straight line canals, but also Y shaped canal, curves or any desirable form needed to evade any obstacle in the process of building a casting line. 

1. A system for transferring liquid metals from a heating furnace to a casting machine wherein the system comprises at least: a central operation panel; a programmable logic controller; a hydraulic central system; a balance hydraulic valve; a level sensor; a heat sensor; a hydraulic cylinder; wherein said central operation panel is operatively connected to said programmable logic controller which controls said hydraulic central system defining a range of action of said balanced valve, wherein at least said level sensor detects the level of liquid metal running through at least a conduit and sends the level detected to said programmable logic controller (PLC), defining said level detected by means of said balanced valve, the tilt degree of a casting furnace.
 2. The system according to claim 1 wherein said at least a conduit comprises at least a canal containing a first profile and a second profile within said first profile.
 3. The system according to claims 1 and 2 wherein a plurality of said canals is abutted each other by attaching means such as nuts and bolts, welding, bridle, defining a modular conduit.
 4. The system according to claim 1 wherein said at least one level sensor is placed in the vicinity of the furnace's outlet.
 5. The system according to claims 1 to 4 wherein said at least one level sensor is configured to measure the level of liquid metal inside the canal.
 6. A canal for forming a conduit to transfer liquid metal from a casting furnace to a casting machine wherein the canal comprises a first U shape profile inside of which there is a second U shape profile, being separated by an insulate layer, defining said second profile a path for transferring liquid metal, and having said first U shaped profile a top cover attached by hinged comprising heating generator means.
 7. The canal according to claim 6 wherein said first U shaped profile is attached to a double T beam.
 8. The canal according to claim 6 wherein the insulate layer is made of fiber glass, ceramic fiber, microporous insulation panels, asbestos, refracting mud or the combination thereof.
 9. The canal according to claim 6 wherein said first U shaped profile is made of a steel alloy.
 10. The canal according to claim 6 wherein said second U shaped profile is made of any of fiber glass, ceramic fiber, microporous insulation panels, asbestos, refracting mud or the combination thereof.
 11. The canal according to claim 6 wherein said heating generator means are electric resistance heating elements enclosed in metal tubes that emit heat in the form of infrared rays.
 12. The canal according to claim 6 wherein a lid is placed on top of first and second profiles protecting the edges of such profiles from breakage.
 13. The canal according to claim 6 wherein said hinged cover attached to said first U shaped profile is actuated by hydraulic means.
 14. The canal according to claim 6 wherein the canal comprises at least a heat sensor placed on either ends of the canal.
 15. The canal according to claim 14 wherein said at least a heat sensor is one of a laser beam sensor, a thermocouple or a combination of both.
 16. A method for controlling the transfer of liquid metal from a furnace to a casting machine wherein comprises the steps of: a) tilting the furnace to a degree until the liquid metal is poured into the conduit; b) obtaining the level information in said conduit by means of a level sensor; c) sending the data obtained by said level sensor to a programmable logic controller; d) controlling the tilt degree of the furnace by comparing the data sent by the level sensor and the data already pre programmed; c) controlling the temperature of the liquid metal in the conduit d) activating the hinged covers in case the temperature is below a level pre settled in the programmable logic controller; e) igniting the heat generator means in the event that the temperature is still below the pre settled level even after the hinged cover was activated; d) regulating the temperature by activating individually said hinged covers and said heat generator means.
 17. The method according to claim 16 wherein comprise the additional steps of: a) increasing the tilt degree of the furnace in the event that said level detector detects a decrease in the level of the liquid metal in the conduit. b) decreasing the tilt degree of the furnace in the event that said level detector detects an increase in the level of the liquid metal in the conduit.
 18. The method according to claim 16 wherein the activation of said hinged cover is strictly related to data supplied by the heat sensor to the programmable logic controller. 